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MOTOR UNIT: A motor (GSE) neuron, plus all of the muscles that neuron innervates.

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TRAPEZIUS MUSCLE: It is innervated by the spinal accessory nerve. Hence with a cervical neck fracture, some people can still shrug their shoulders, even though they've lost upper-limb innervation, due to residual innervation from this nerve.

TRIANGLE OF AUSCULTATION (N399a): On the medial back, it is an area of little muscle and hence a good place to listen to the lungs.

QUADRANGULAR SPACE (N401b): Just medial to the surgical neck of the humerus on the posterior side.

TRIANGULAR SPACE (N401a, N401b): Anterior aspect, medial to the neck of the humerus.

TRIANGULAR INTERVAL (N401b): Between the two heads of the triceps muscle, inferior to the teres major.

SCAPULA: The shoulder blade.

Deltoid Muscle: It inserts on the Deltoid Tuberosity of the humerus and has multiple actions

Abduction of the Arm:

PECTORALIS MAJOR: Aids in both flexing and extending the arm, depending on part of muscle.

CLAVIPECTORAL FASCIA (N403): Fascia separating the pectoralis major from pectoralis minor, and overlying the pecs, the serratus anterior, and latissimus dorsi muscles. It goes from the pec-minor to the clavicle.

CEPHALIC VEIN CLINICAL: A surgeon may pass a fine tube through the Cephalic Vein ------> Axillary Vein ------> Subclavian ------> SVC ------> Heart to withdraw blood.

THE AXILLA (N404, N403b):

AXILLARY ARTERY (N402a): Branches of the Axillary Artery.

AXILLARY VEIN (N175): The union of the basilic and deep brachial veins. It then joins with the Cephalic Vein to become the Subclavian Vein.

THYROCERVICAL TRUNK (N402a): An arterial branch that comes off the subclavian artery, before it turns into the Axillary Artery. It has the following branches:

AXILLARY LYMPH NODES (N456): The apical group is the most crucial for spreading of breast cancer. If it has gotten to the axillary group, you is in trouble.


MEDIAN NERVE: Formed by the union of the anterior divisions of the lateral and medial cords. It is the bottom-middle part of the "M"

DUCHENNE-ERB PARALYSIS: Damage to the Upper Trunk of the Brachial Plexus

KLUMPKE'S PARALYSIS: Damage to the lower trunk (C8-T1).

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THE HUMERUS (N396, N397)

Cutaneous Innervation of the Arm (N454):

BRACHIAL ARTERY (N409): Supplies the arm.

MUSCULOCUTANEOUS NERVE: The major innervator of the arm.

Intermuscular Septa: Fibrous sheath that separates the anterior and posterior compartments of the forearm.


ULNAR ARTERY (N409, N422): One of the terminal branches of the Brachial Artery.

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BRACHIORADIALIS: CLINICAL -- it may become damaged during a distal radial fracture, because it inserts on the styloid process of the radius.

COMMON EXTENSOR TENDON: The origin of the superficial extensor forearm muscles. It hooks onto the lateral epicondyle and supracondylar ridge of the humerus.

POSTERIOR INTEROSSEUS NERVE: The Deep Branch of the Radial Nerve. It innervates most muscles of the extensor forearm.

POSTERIOR INTEROSSEUS ARTERY: Supplies the extensor forearm muscles and travels with the Posterior Interosseus Nerve. It is a branch of the Common Interosseus Artery, which comes from the Ulnar Artery.

EXTENSOR RETINACULUM (N443): The sheath that covers all of the extensor tendons going into the wrist.

EXTENSOR DIGITORUM: These tendons cross over the MCP, PIP, and DIP joints -- one tendon going over all joints. This is different than the flexor digitorum.

ANATOMICAL SNUFFBOX: In between the Extensor Pollicis Longus and Extensor Pollicis Brevis. The Abductor Pollicis Longus is directly lateral to it.

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MEDIAN NERVE (N448): Lies in between the flexor digitorum superficialis and flexor digitorum profundus in the forearm.


RADIAL NERVE (N450, N451): Enters the forearm by traveling over the lateral epicondyle. Splits into two branches.

T1: INTRINSIC MUSCLES -- All intrinsic muscles of the hand are supplied by T1 fibers, whether from the Ulnar or Radial nerves.

LATERAL ANTEBRACHIAL CUTANEOUS NERVE: From the Musculocutaneous Nerve, it innervates the lateral part of the anterior forearm.

MEDIAL ANTEBRACHIAL CUTANEOUS NERVE: From the medial cord of the brachial plexus, it innervates the medial part of the cutaneous flexor forearm.

RADIAL ARTERY (N409, N422): One of the terminal branches of the Brachial Artery.

ULNAR ARTERY (N409, N422): One of the terminal branches of the Brachial Artery.

FLEXOR RETINACULUM (N433b, N434a): The sheath that contains the flexor tendons on the anterior wrist.

MOBILE WAD: The lateral compartment of the flexor forearm, which is more loosely connected than the other compartments. It contains two muscles:

PALMARIS LONGUS MUSCLE: Absent in about 30% of people, and a good candidate for surgical tendon transfers when it is present.

FLEXOR DIGITORUM: Acts differently than the extensor digitorum.

SPACE OF PARONA: The potential space between the superficial and deep groups of anterior muscles -- essentially between the Flexor Digitorum Superficialis and Flexor Digitorum Profundus.

FASCIA ANTEBRACHIALIS: Thick fascial plane over the anterior forearm.

INTEROSSEUS MEMBRANE: Between the radius and ulna, the posterior limit to the anterior compartment. The Anterior Interosseus Nerve and Artery, and the Flexor Digitorum Profundus, are directly superficial to it.

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Types of Joints: Joints are structures that connects bones together.

Hilton's Law: The nerves supplying a join also supply the muscles moving that joint and the skin covering those muscles.

DEGREE'S OF FREEDOM: The more mobile a joint (i.e. the more degrees of freedom), the less stable it is.

CLINICAL -- Injuries / Diseases of the Joints:

CONJUNCT ROTATION: Instinctive or automatic rotation of the forearm, as demonstrated by Codman's paradox, where you hold your palm to your side, abduct it, rotate it anteriorly, and bring it back to your body, to discover that it is now facing the other way.

ADJUNCT ROTATION: Deliberate rotation of the joint, such as when you point your hands laterally and then try to abduct your arm.




RADIOCARPAL JOINT (WRIST) (N429): The Radius articulates with the Carpal Bones -- not the Ulna at all!

Joint of Knuckles and Fingers:

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Movements of the Fingers:

Force Transduction through the Hand and Arm:

Common Wrist Fractures:

Extrinsic Muscles of the Hands: Mostly concerned with grip.

Intrinsic Muscles of the Hands: Concerned with manipulation of the digits. All of them are basically innervated by T1.

PALMAR APONEUROSIS: Deep to the skin and fascia. It holds it down, so that the skin on the palm is tight and hairless.

CLINICAL -- DUPUYTREN'S CONTRACTURE: Flexion of the 4th and 5th digits, resulting from progressive shortening of the palmar aponeuroses, from hypertrophy and hyperplasia. Unknown cause.

FIBROUS FLEXOR SHEATHS (N435): Strong sheath covering the long tendons going into the hand, distal to the flexor retinaculum.

SYNOVIAL FLEXOR SHEATHS (N435): The fibrous sheaths are enclosed in synovial sheaths in areas where there is friction. Primarily:

RADIAL BURSA (N435, N436):

ULNAR BURSA (N435, N436):

CLINICAL -- HORSESHOE INFECTION: Infection spreading from little finger to thumb or vice versa, as a consequence of the communication between the radial and ulnar bursae.

CLINICAL: DORSAL SUBCUTANEOUS SPACE will receive lymph from the palmar aspect of the hand. Thus a hand-infection can easily result in swelling on posterior aspect of the hand, in which case it would be lymph -- not pus -- so don't incise it.

SUPERFICIAL PALMAR ARCH (N439a): Main arterial supply to the hand.

Literally it is formed by a continuation of the artery, and it anastomoses with the Superficial Palmar Branch of the Radial Artery.

It gives off Common Palmar Digital Arteries ------> Proper Palmar Digital Arteries

DEEP PALMAR ARCH (N439b): Lies deep to the flexor retinaculum.

This is formed by the radial artery, and it anastomoses with the terminal ulnar artery.

It gives off the Palmar Metacarpal Arteries ------> Proper Palmar Digital Arteries

DORSAL CARPAL ARCH: From the dorsal carpal branches of the Radial and Ulnar arteries.

It gives off the Dorsal Metacarpal Arteries ------> Dorsal Digital Arteries.

THENAR SPACE: The area deep to the 1st lumbrical muscle and the 2st flexor tendon, in the palm of the hand.

MIDPALMAR SPACE: The medial part of the deep palm of the hand, deep to the rest of the flexor tendons. It is next to the Thenar Space.

A SEPTUM separates the Thenar from MidPalmar spaces.


LUMBRICALS: They provide stability to the digits.

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SPACE OF PARONA COMPRESSION: Veins are subject to compression when swelling or fluid buildup occurs in any potential space. This causes blood to backflow, which causes the following course of events.

FASCIOTOMY: Cutting through the fascia which is causing the compartment syndrome, thereby relieving the pressure and hopefully the compartment syndrome.

SATURDAY NIGHT SYNDROME: Drunk person falling asleep on elbow and hence on ulnar nerve. Wake up the next morning and the ulnar nerve is dead.

CORACOBRACHIALIS SYNDROME (N447): Loss of the Musculocutaneous Nerve where it runs through the Coracobrachialis Muscle. If the muscle dies, then nerve dies with it.

SUPINATOR CHANNEL SYNDROME (N419): Compression of the Deep Branch of the Radial Nerve between the Superficial and Deep Heads of the Supinator, and the Lateral Epicondyle.

SUPRACONDYLAR SYNDROME: Entrapment of the Median N. beneath the Ligament of Struthers, which connects the Supracondylar Process to the Medial Epicondyle.

PRONATOR TERES SYNDROME (N420): Entrapment of Median N. passing between the Deep and Superficial Heads of the Pronator Teres.

MARTIN-GRUBER ANASTOMOSIS: Connection between the Median and Ulnar nerves in the palm of the hand, in about 30% of population. When the connection is there, it is mainly a motor connection.

CARPAL TUNNEL SYNDROME: The Median Nerve passes deep to the flexor retinaculum. If it is entrapped, carpal tunnel syndrome results.

CUBITAL TUNNEL SYNDROME: Compression of the Ulnar Nerve between the two heads of origin of the Flexor Carpi Ulnaris.

GUYON'S CANAL SYNDROME (N432): Compression of the Ulnar Nerve in Guyon's Canal, between the Volar Carpal Ligament and the Flexor Retinaculum.

DUPUYTREN'S CONTRACTURE: Progressive shortening of the palmar aponeuroses, from hypertrophy and hyperplasia. Unknown cause.

TENOSYNOVITIS: Not to be messed with. Inflammation of the tendons in the synovial joints, which can spread proximally all the way to the elbow.

DEQUERVAIN'S DISEASE: A specific tenosynovitis of the first extensor compartment, which transmits the Extensor Pollicis Longus and Brevis.

SCAPHOID FRACTURE: If the scaphoid is fractured, there is potential for avascular necrosis in 1/3 of all people, because blood comes from only one place -- the distal end.

TRIGGER FINGER: Swelling of the fibrous sheaths going around the tendons, such that, when the tendon is on one side of the swelling, such that the finger is flexed, it will stay that way and you can't extend it. Then you can pull real hard to get the tendon past the "bottleneck" to the other side of the swelling, such that the finger extends, and then you can't flex it again!

RAYNAUD'S DISEASE: Vascular problem of too high of sympathetic tone, which can cause complications in the hand.

VARUS: A bone-fracture that creates angulation toward the midline of the body.

VALGUS: A bone-fracture that creates angulation away from the midline of the body.





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Copyright 1999, Scott Goodman, all rights reserved